Vertical cavity surface emitting lasers (VCSELs) represent a versatile coherent light source that has made tremendous impacts on numerous modern technological applications including data communication, optical mice, laser printing, and, more recently, biomedical imaging and sensing, in which VCSELs provided many inimitable advantages over light emitting diodes or edge-emitting lasers including low power consumption, small beam divergence, circular beam profile, or facile integration into two-dimensional (2D), surface-emitting arrays (J. S. Harris et al., Semicond. Sci. Technol. 2011, 26; K. Iga, Jpn. J. Appl. Phys. 2008, 47, 1; K. Iga, Proc. IEEE 2013, 101, 2229; K. D. Choquette and H. Q. Hou, Proc. IEEE 1997, 85, 1730).
Although VCSELs in their conventional formats operating on their growth wafer have been successfully exploited over the past decades, the ability to incorporate VCSELs on non-native substrates and heterogeneously assemble them with dissimilar materials and devices into integrated systems hold great potential for a variety of unconventional utilities that are not available in traditional VCSEL technologies (C. Dagdeviren et al., Nature Communications 2014, 5; K.-I. Jang et al., Nature Communications 2014, 5; M. Kaltenbrunner et al., Nature 2013, 499, 458; D. Son et al., Nat. Nanotechnol. 2014, 9, 397; S. Xu et al., Science 2014, 344, 70).
In this regard, a recent work by Kang et al. (Adv. Optical Mater. 2014, 2, 373) successfully demonstrated materials design and fabrication processes of releasing ultrathin, microscale VCSELs (micro-VCSELs) from the growth wafer and incorporating them into arrays of interconnected devices over unlimited choices of non-native substrates including silicon, glass or a thin sheet of plastics without compromising intrinsic materials properties. While such novel device platforms of micro-VCSELs promise to accelerate accomplishing many unprecedented applications with unique advantages including programmable spatial layouts, efficient utilization of expensive epitaxial materials, as well as thin, lightweight, and flexible constructions, devices printed on a substrate with a low-to-moderate thermal conductivity exhibited a substantial reduction of the optical output power because of comparatively limited heat removal rate and resultant temperature increase in the laser cavity (D. Kang et al., Adv. Optical Mater. 2014, 2, 373; S. Matsuo et al., Electron. Lett. 1997, 33, 1148; H. Jeong and K. D. Choquette, 2013 IEEE Photonics Conference, Bellevue, 2013).
Although thermally-induced performance degradation is a common challenge for most solid-state devices working on plastics (M. Kaltenbrunner et al., Nature 2013, 499, 458; T. I. Kim et al., Small 2012, 8, 1643; K. Kuribara et al., Nature Communications 2012, 3; T. I. Kim et al., Appl. Phys. Lett. 2014, 104; Y. H. Li et al., Proc. R. Soc. A 2013, 469; Y. H. Li et al., J. Appl. Phys. 2013, 113), it becomes much more serious in VCSELs as it can lead to a complete shut-off of the device functionality due to the remarkably sensitive nature of lasing against the temperature variation of the cavity, associated with a spectral mismatch between emission of gain medium and cavity resonance at elevated temperatures (H. Jeong and K. D. Choquette, 2013 IEEE Photonics Conference, Bellevue, 2013; G. Hasnain et al., IEEE J. Quantum Electron. 1991, 27, 1377; R. A. Morgan et al., Electron. Lett. 1991, 27, 1400). Development of novel integration pathways to allow implementation of VCSELs in mechanically compliant formats without sacrificing their wafer-level performance is therefore critically important to realize the full potential of this technology for future applications in flexible and wearable optoelectronics.